1. Field of the Invention
This invention pertains to a new honeycomb structure and to a new method of making structural honeycomb.
2. The Prior Art
Honeycomb is generally described as a structure of hexagonal thin walled cells. Most honeycomb structural panels have a central core of thin walled cells, and a structural skin secured on the outer surface of each side of the core, with the skins being normal to an axis of the cells. The cells can be either exactly or approximately hexagonal, or square or of some other geometric shape.
The most commonly encountered honeycomb structures in nature are bee, wasp and hornet made structures.
Man made honeycomb structures are being used for many purposes. The typical use will require light weight, stiffness and high strength. Typical actual specific honeycomb uses are floors in aircraft and load carrying vehicles, platforms, walls and building panels, doors, sporting equipment, pallets and skids, and packaging. These specific uses will typically have a structural skin on both sides of the core.
Honeycomb core with a skin on only one side also has utility and is used for material handling and distribution, ammunition storage, fuel cell cores, molding and for other purposes.
A wide variety of materials have been and are used as outer structural skin material, ranging from simple cardboard to the most esoteric fiber filled resins of the aerospace and armor industries.
Material usage in the honeycomb core has, however, been restricted to lesser performance materials such as paper, cardboard, and aluminum. All these core materials have corrosion suceptibility problems and none are effectively useable in water and many other corrosive liquids and environments.
The paper and cardboard cores degrade when wet, and both the paper and aluminum cores are attacked by bases or acids.
Usage of these honeycomb structures has been limited to dry and somewhat protected environments.
The core materials being used have not been of particularly high strength. The aluminum honeycomb must use an alloy that can be formed to make the cellular structure and the extremely high strength relatively brittle alloys used for flat panel aerospace applications cannot be effectively used.
There is only one known example of fiber reinforced resin honeycomb core in use, and it is available under the Hexcel brand name. This particular material is a long fiber made into something resembling paper, which is provided in a soft non-rigid form. Specifically it's in a folding accordian type structure that can be compressed and stretched and matched to single plane or compound contours. It is available in a maximum thickness of about 6 mm (0.24 inch) and costs about $18 per square foot. This material is then bonded and made rigid by being dipped one or more times in a penetrating resin. The more times you dip this core, the more resin you build up. The specific end uses of this core material are not fully known but its cost must restrict its effective use to aerospace and/or military end uses.